The present invention relates to a drafting system with a drive arrangement with a regulating device for regulating mass variations in a fibre mass supplied from a supply source to a drafting system in which arrangement the mass variations are detected by at least one measuring device coordinated to the drafting system and transmitted to a control unit.
In practice regulating drafting systems are known form the following publications:
JP-Gbm-5017/78 Nihon Keikzai KK PA1 JP-A-155231/177 Nagoya Kinzoku Harinuno KK PA1 DE-A-1931929 Zinser PA1 DE-A-2230069 Texcontol PA1 CH-B-599993 Graf PA1 EP-C-354653 Hollingsworth PA1 EP-A-544425 Hollingsworth PA1 EP-A-604137 Hollingsworth PA1 EP-A-617149 Grossenheiner Textilmaschinenbau GmbH PA1 EP-A-643160 Howa Machinery, Ltd PA1 EP-A-692560 Chemnitzer Spinnereimaschinenbau GmbH PA1 US-B-5400476 Myrick-White, Inc.
A conventional card operates at a constant (pre-settable) production rate, i.e. the fibre sliver is delivered at a predetermined speed from the delivery arrangement The function of a regulating drafting system implies that the draft is variable (controllable). Provision of a large sliver storage device between the card delivery system must be variable. This, however, creates problems concerning the drive for the sliver deposition or coiler system, the inertia of which is relatively considerable, arranged downstream from the drafting system.
Various devices are known, e.g. from the DE-OS-19 19 929, in which arrangement sliver storage device is arranged between the card and a regulating drafting system. This can be seen in particular in the FIGS. 3 and 4 of the DE-OS reference. Adjoining the regulating drafting system a sliver storage device is arranged driven by a separate motor. The measured values determined by the pair of measuring rolls upstream from the regulating drafting system are compared to the preset desired values. The resulting deviation signal serves for controlling the drive motor for the intake pair of rolls of the drafting system in order to adapt the draft ration, and to level out thin and thick places respectively. At the same time, this signal transmitted to the control device for the drive of the fibre sliver source, or of the card respectively, in such a manner that this drive also can be adapted correspondingly. The reaction of the card however, is subject to substantially higher inertia than the drafting system. The resulting differences in the material delivery, and in the material intake respectively, are leveled out in the sliver storage device adjoining the card. The storage device in this arrangement is provided with sensors for scanning the contents of the storage device. Based on the contents determined by the sensors in the sliver storage device, the drives of the fibre sliver source (card) and of the fibre sliver take-up device (coiler) are changed accordingly in such a manner that the contents of the fibre sliver storage device is maintained substantially constant. This adaptation of the two drives however, results in additional differences, especially as the elements of the card (e.g. the card main drum) are subject to different inertia influences other that the elements of the sliver depositing device (coiler).
Furthermore, from the previously published DE-A1-44 24 490 a co-ordination of cards is known in which a storage device is coordinated to each card downstream and in which the card slivers delivered by the individual storage devices after passing through a drafting system are delivered to a common sliver deposition device or coiler. In order to compensate for the loss of one of the card slivers supplied to the drafting system the delivery speed of the drafting system is reduced until the missing card sliver has been re-inserted. In this arrangement, a scanning sensor is coordinated to each individual card sliver. Owing to the reduction in delivery speed, corresponding to the loss of one card sliver, the fibre sliver reserve for the draw frame is exhausted more slowly than in the normal operating mode at higher intake speeds. In the example shown, an increase of the card delivery speed also is proposed if the fibre sliver storage device arranged downstream is depleted in excess of a predetermined value in such a manner that the operation of the subsequent draw frame is not jeopardized. The arrangement shown is suitable for levelling out massive short term variation (loss of sliver). Levelling out long term deviations however, is not envisaged using this arrangement, or is solved unsatisfactorily only.
For levelling out long period mass deviations in the fibre sliver delivered by the card it is proposed in DE-A1 29 12 576 that the thickness of the fibre sliver delivered by the card be measured and compared to a pre-set desired value. The signal thus determined is used in controlling the material supply device (feed roll) arranged upstream from the card. Owing to this arrangement, long period deviations in the mass of the card sliver delivered can be reacted on. Avoiding and eliminating of short wave deviations e.g. using a regulated drafting system is not envisaged in the arrangement described. The action in the control of the drive of the feed roll for compensating for long period mass deviations becomes effective, however, only after a major time delay.
The solutions proposed thus far generally provide the drafting system for levelling out short term variations in the fibre sliver. The correspondingly propose application of a measuring sensor at the intake of the drafting system.
Similar problems are encountered on other machines also, e.g. on the combing machine, if directly downstream from a textile processing unit a regulated drafting system is arranged which is driven at a regulated variable intake speed.